Enterovirus 71 (EV71) is a member of the Enterovirus genus of the Picornaviridae family. EV 71 is the major cause of hand-foot-and-mouth disease (HFMD) in children. EV71 infection can be accompanied by a series of syndromes with or without central nervous system involvement including herpangina, aseptic meningitis, poliomyelitis-like paralysis and possibly fatal encephalitis. EV71 is a single-stranded RNA virus with a 7500-bp genome, enclosed by a capsid comprised of four coat proteins, VP1-VP4. The capsid protein VP1 of EV71 was reported to be the major antigenic coat protein and potent to act as an antiviral subunit vaccine, and VP4 to be an anchor-protein, linking VP1 to VP3 to form intact viral particles [Chow M et al., Nature 1987; 327: 482-486]. Since the viral particles (VPs) belonging to the Picornaviridae family can withstand human gastric acid and are infectious below pH 3.0, the VP1 would be expected as an antigen of an oral vaccine against entervirus.
Based on the genetic analysis of the EV71 epidemic in Taiwan, the sequences in the focal regions of 3C and 3′-non-coding region are different between the EV71 isolates from fatal cases and non-fatal cases [Shih SR et al., Virus Res 2000; 68: 127-136]. It was indicated that the VP1 protein of the EV71 was potential as an antigen in both the diagnosis and subunit vaccine development against EV71 [Yu CK et al., J. Biomed. Sci. 2000; 7:523-528]. Purified recombinant VP1 protein was defined as a neutralization determinant, with the ability to trigger vaccine-mediated immune responses in either Coxsackie virus B3-infected mice or swine [Henke A et al., Antiviral Res 2001; 49:49-54]. A VP1 subunit vaccine was produced in either bacteria or transgenic plants, which was effective against EV71 and foot-and-mouth disease virus [Wu CN et al., Vaccine 2002; 20:895-904]. However, it is still desired to develop a good vaccine effective for protection against EV71 and a feasible method for mass production of the vaccine antigen.